Liquid level detecting device

ABSTRACT

The present invention aims at attaining a liquid surface level detecting apparatus, which can be used in various detection targets and usage environments without selecting a detection target, can efficiently irradiate a light to a liquid surface level detecting unit and detect a variation in a light reception amount of a light receiving means at a high sensibility, and can be excellent in durability, easy to manufacture, and be actually used. By placing a light shielding means  14  so as not to directly irradiate the light from a light emitting means  12  to a light receiving means  13 , the light from the light emitting means is scattered by an optically scattering means  16 , and a part of that scattering light is radiated to an outside by the liquid surface level detecting unit on a light radiating means (an optically transmitting member)  11 . On the other hand, the scattering light, which is reflected without being radiated, is received by the light receiving means, and the change in that light reception amount is detected. Consequently, if a liquid  17  exists in the outside, a light amount, which is reflected by a boundary between the liquid and the light radiating means and returned to an inside of the light radiating means, is reduced, and the light reception amount in the light receiving means is also reduced. Thus, by measuring the change in the light reception amount, it is possible to detect a liquid surface level of the liquid.

TECHNICAL FIELD

[0001] The present invention relates to a liquid level detecting devicewhich is also referred to a liquid surface level detecting apparatus,which is kept in a vessel such as a tank, a pipe, a drum can or thelike, for detecting a liquid surface level of a liquid that can not beeasily checked from outside, and more particularly to an apparatus forcarrying out a liquid surface level detection by using a scatteringlight.

BACKGROUND ART

[0002]FIG. 7 is a sectional view of one example of a conventional liquidsurface level detecting apparatus that uses a reflection of light by aprism. A liquid surface level detecting apparatus 100 shown in FIG. 7 isprovided with: an optically transmitting member 102 which has an end(hereafter, referred to as a prism section 101) cut to a predeterminedshape and is made of bar-shaped fluoro-resin or glass and the like; alight emitting means 103 for emitting the light to a longitudinaldirection of the optically transmitting member 102 toward the prismsection 101; a light receiving means 104 for receiving a reflectionlight which is returned to the longitudinal direction of the opticallytransmitting member 102 from the prism section 101 after the lightemitted by the light emitting means 103 is reflected by the prismsection 101; and an IC 105 for measuring a light amount of thereflection light received by the light receiving means 104 andoutputting its measured result.

[0003] Also, in such a way that the light emitted by the light emittingmeans 103 can be efficiently received by the light receiving means 104,the predetermined shape of the prism section 101 is defined. Forexample, it is defined such that the emitted light is totally reflectedby the prism section 101, and such that the total reflection light isreturned to the light receiving means 104. That is, when a refractiveindex of the optically transmitting member 102 is assumed to be nt and arefractive index of air is assumed to be n_(s) (n_(s)≈1), in such a waythat an irradiation angle of the light from the light emitting means 103becomes sin θ_(o)=n_(s)/n_(t), a predetermined shape of a low end of theprism section 101 and the installation positions of the light emittingmeans 103 and the light receiving means 104 are defined.

[0004] If a liquid surface level 107 of a liquid 106 is brought intocontact with a portion to which the light of the prism section 101 isirradiated, a refractive index of an outside of the prism section 101 ischanged (usually, since a refractive index of the liquid 106 is greaterthan the air, the refractive index of the outside becomes greater), atotal reflection angle θ_(o) is changed. Consequently, the light fromthe light emitting means 103 is radiated to an inside of the liquid 106,and the light amount returned to the light receiving means 104 islargely reduced. By measuring the change in this light amount, the factthat the liquid surface level 107 is brought into contact with the lowend is detected.

[0005] However, in the liquid surface level detecting apparatus 100 ofFIG. 7, a liquid surface level detecting unit exists in the prismsection 101 at the low end. Thus, once the liquid surface level of theliquid 106 is detected, liquid drops continue to be deposited. Hence,there may be a case that an erroneous operation is induced in the liquidsurface level detection or that the liquid surface level detection cannot be done. A liquid surface level detecting apparatus that tries toimprove this problem is a liquid surface level detecting apparatus shownin FIG. 8 as described below.

[0006]FIG. 8 is a sectional view of one example of the conventionalliquid surface level detecting apparatus that uses the total reflectionlight. A liquid surface level detecting apparatus 200 shown in FIG. 8 isprovided with: an optically transmitting member 201 which is hollow andmade of bar-shaped fluoro-resin or glass and the like; a light emittingmeans 202 and a light receiving means 203 which are placed in the hollowsection therein and composed of optical fibers and the like; a lightshielding wall 204 for avoiding a light from the light emitting means202 from being directly irradiated to the light receiving means 203; andan IC 205 for measuring a light amount received by the light receivingmeans 203 and outputting its measured result.

[0007] Also, if a liquid 206 does not exist in an outside (namely, ifthe outside is air), in such a way that the light is totally reflectedby an outer wall on a side of the optically transmitting member 201,angles of those light emitting means 202 and light receiving means 203are established. That is, when a refractive index of the opticallytransmitting member 201 is assumed to be nt and a refractive index ofthe air is assumed to be ns (n_(s)≈1), in such a way that the light isinputted at an input angle larger than a critical angle θ_(o) in whichan irradiation angle of the light from the light emitting means 202 isdetermined by sin θ_(o)=n_(s)/n_(t), the light emitting means 202 isplaced. Also, the light receiving means 203 is placed at a positionhaving the same reflection angle as the input angle from the lightemitting means 202, in such a way that the total reflection light fromthe outer wall of the optically transmitting member 201 can beefficiently received.

[0008] As mentioned above, if the outside is the air, the light from thelight emitting means 202 is totally reflected by the outer wall of theoptically transmitting member 201 and received by the light receivingmeans 203. However, if a liquid surface level 207 is brought intocontact with a location (hereafter, referred to as a total reflectionunit) where the light of the side of the optically transmitting member201 is totally reflected, the refractive index of the outside of theabove-mentioned optically transmitting member 201 is changed, and thecritical angle θ_(o) is changed. Consequently, the light from the lightemitting means 202 is radiated to an inside of the liquid 206, therebygreatly reducing a light amount returned to the light receiving means203. By measuring the change in this light amount, the fact that theliquid surface level 207 is brought into contact with the totalreflection unit is detected. In the liquid surface level detection usingsuch a total reflection, if the liquid 206 exists in the totalreflection unit, the total reflection of the light is not induced, andits reflection light amount is dramatically changed. Hence, the changeamount in the light amount of the light receiving means is great, and itis possible to carry out the liquid surface level detection whoseprecision is high.

[0009] Also, Japanese Laid Open Patent Application (JP-A 2000-329607)and Japanese Laid Open Patent Application (JP-A 2000-321116) disclose aliquid surface level sensor for scattering a propagation light, andconsequently measuring an attenuation amount of the propagation light,and then detecting a liquid surface level. For example, Japanese LaidOpen Patent Application (JP-A 2000-329607) discloses a liquid surfacelevel sensor 300 that uses a scattering light in which the propagationlight is scattered as shown in FIG. 9.

[0010] This liquid surface level sensor 300 passes and scatters thepropagation light through a light scattering member (particle body) 301,and consequently generates the scattering light, radiates the scatteringlight from a sensing section 302 to outside, and measures theattenuation amount of the propagation light attenuated by the influenceof the liquid existing in the outside, and then detects the liquidsurface level. Also, besides FIG. 9, for example, as shown in FIG. 10, aconfiguration in which optically transmitting materials whose refractiveindexes are different are placed on the entire U-shaped section isdisclosed.

[0011] However, the liquid surface level detecting apparatus shown inFIG. 8 carries out the liquid surface level detection through the totalreflection. For example, if the liquid surface level detection of aliquid having a high viscosity coefficient is once carried out and thatliquid surface level detecting apparatus is again used to carry out theliquid surface level detection, the liquid drops are deposited on thetotal reflection unit. Thus, the total reflection on the totalreflection unit is never induced. Hence, there is a problem that theliquid surface level detection is impossible unless the liquid drops areremoved. Also, if oil film and contaminant are deposited on the totalreflection unit, similarly, there is a problem of a possibility that anerroneous operation is induced.

[0012] Also, in the liquid surface level detecting apparatus shown inFIG. 8, since the establishment of the critical angle to define thetotal reflection is carried out in the prism section and the totalreflection unit, it is necessary to establish the various conditionssuch as the angle of the prism section, the installation positions andinstallation angles of the light emitting means and the light receivingmeans, the distance from the light emitting means to the light receivingmeans (namely, the distance in the longitudinal direction of the lightshielding wall), and the light emitting angle and the light receivingangle, and the like. For example, such as the case that even oneomission from those conditions disables the liquid surface leveldetection and the like, there is a problem that the durability againstthe deterioration in the liquid surface level detecting apparatus causedby the various usage conditions, such as flaw and damage resulting fromshock from the outside, acid-base property and the like, is very weak.Also, since those various conditions need to be established, there is aproblem that the manufacturing of the liquid surface level detectingapparatus becomes precise and difficult.

[0013] Also, the liquid surface level detecting apparatus shown in FIG.8 is established, for example, in such a way that with regard to theinitial state at which the outside of the liquid surface level detectingunit is the air, the total reflection is induced, and within thepredetermined detection target (liquid), the total reflection is notinduced. On the other hand, such a detection target is differentdepending on a usage environment. Thus, there is a problem thatdepending on the establishment of the critical angle θ_(o), although theliquid having a high refractive index can be detected, the liquid havinga low refractive index cannot be detected. Also, the conventional liquidsurface level detecting apparatus has a problem that an erroneousoperation is induced if the detection target is colored liquid.

[0014] Also, the liquid surface level detecting apparatus shown in FIG.8 has the following problem. For example, it can detect a boundarybetween two layers of air and liquid. However, if it tries to detect aboundary between three layers of air, oil and water, it must use twokinds of liquid surface level detecting apparatuses. That is, one is aliquid surface level detecting apparatus which is established such thatthe change of the presence or absence of the total reflection is inducedon the boundary between the air and the oil, and the other is a liquidsurface level detecting apparatus which is established such that thechange of the presence or absence of the total reflection is induced onthe boundary between the oil and the water. By the way, in thisspecification, a boundary between a liquid phase and a gaseous phase anda boundary between different two liquid phases are referred to as aliquid surface.

[0015] Also, the liquid surface level sensor shown in FIG. 9 has thestructure that the light emitted from the light emitting means isdirectly inputted to the light receiving means, and the light receivingmeans receives the considerable quantity of propagation light, evenbefore the liquid surface level detection. The light directly inputtedto the light receiving means from this light emitting means does notcontribute to the liquid surface level detection and further greatlyreduces the precision in the liquid surface level detection. Inparticular, at the time of the liquid surface level detection, if thescattering light amount radiated to the outside from the sensing section(namely, the attenuation amount of the propagation light by the lightreceiving means) is small, a variation rate of the light receptionamount of the light receiving means (=the light reception amount afterthe liquid surface level detection/the light reception amount before theliquid surface level detection) becomes very small. Thus, it is verydifficult to measure that variation. Hence, there is a problem that thisis not practical.

[0016] Thus, in particular, if a distance L of the sensing section ismade shorter in order to improve the precision in the liquid surfacelevel detection, the scattering light amount radiated to the outsidefrom the sensing section is inevitably reduced, thereby further reducingthe variation rate of the light reception amount of the light receivingmeans. Hence, this liquid surface level sensor has a problem that unlessthe distance L of the sensing section is set to be considerably large,the liquid surface level detection is impossible and the precision inthe liquid surface level detection is very low.

[0017] Also, as shown in FIG. 10, the liquid surface level sensor, inwhich the optically transmitting materials having the differentrefractive indexes are placed on the entire U-shaped section and thelight is radiated from the U-shaped section, has the structure that thepropagation path of the light is especially curved, and most of thepropagation light is leaked as the scattering light to the outside,which results in the extreme reduction in the light reception amount ofthe light receiving means. Also, moreover, even if the liquid surfacelevel is detected, it is impossible to accurately specify the liquidsurface level. Thus, only the liquid surface level detection of the verylow precision can be done. Hence, there is a problem that this is notpractical.

DISCLOSURE OF THE INVENTION

[0018] In view of the above-mentioned problems, it is therefore anobject of the present invention to provide a liquid surface leveldetecting apparatus, which can be used in various detection targets andusage environments without selecting a detection target, and even withregard to a liquid having a high viscosity, can continue to surelydetect that liquid surface, and is excellent in a durability and easy tomanufacture. Also, the present invention aims at providing the liquidsurface level detecting apparatus, which can efficiently irradiate alight to a liquid surface level detecting unit and detect a variation ina light reception amount of a light receiving means at a highsensibility and can carry out a liquid surface level detection at anactually excellent sensibility.

[0019] In order to attain the above-mentioned object, the presentinvention is designed such that by placing a light shielding means forpreventing a light from a light emitting means from being directlyradiated to the light receiving means, a part of a scattering lightscattered by an optically scattering means is outputted to an outside bythe liquid surface level detecting unit, and on the other hand, thescattering light, which is reflected and returned without beingradiated, is received by the light receiving means, and a change in itslight reception amount is detected.

[0020] That is, the present invention provides a liquid surface leveldetecting apparatus for detecting a liquid surface level of a liquidexisting in an outside, including:

[0021] a light emitting means for emitting a light;

[0022] an optically scattering means for scattering the light emitted bythe light emitting means;

[0023] a light radiating means having a liquid surface level detectingunit for radiating a part of a scattering light scattered by theoptically scattering means to an outside of the optically scatteringmeans;

[0024] a light receiving means for receiving the scattering light whichis reflected by and returned from a boundary of the outside of theoptically scattering means or the light radiating means without beingradiated by the light radiating means; and

[0025] a light shielding means for shielding the light so that the lightfrom the light emitting means is not directly irradiated to the lightreceiving means,

[0026] wherein if the liquid exists in the outside, a radiation lightamount to the outside of the light radiating means is changed, and thatchange is detected on the basis of the light reception amount of thelight receiving means, thereby detecting the liquid surface level of theliquid.

[0027] Also, moreover, establishing a predetermined angle and placingthe light emitting means or light receiving means is a preferableimplementation of the present invention.

[0028] Also, moreover, placing a plurality of light receiving means is apreferable implementation of the present invention.

[0029] Also, moreover, arraying the plurality of light receiving meanson a substantially flat surface is a preferable implementation of thepresent invention.

[0030] Also, moreover, covering the light shielding means with a filmfor light reflection in order to protect the light from being absorbedby the light shielding means is a preferable implementation of thepresent invention.

[0031] Also, moreover, enabling a standard light reception amount in thelight receiving means to be established on the basis of a kind of theliquid, and comparing a light reception amount of the light receivingmeans with the standard light reception amount, and consequentlydetecting the liquid surface level of the liquid is a preferableimplementation of the present invention.

[0032] Also, moreover, placing the optically scattering means around alight emitting unit of the light emitting means is a preferableimplementation of the present invention.

[0033] Also, moreover, placing the optically scattering means around theliquid surface level detecting unit to which the light from the lightemitting means is irradiated.

[0034] Also, moreover, the fact that the optically scattering means issilicon rubber is a preferable implementation of the present invention.

[0035] Also, moreover, the fact that the light radiating means isper-fluoro-alkoxy is a preferable implementation of the presentinvention.

[0036] Also, moreover, using a tungsten lamp as the light emitting meansand using a glass optical fiber as the light receiving means are apreferable implementation of the present invention.

[0037] Also, moreover, by dipping the light radiating means into theliquid and measuring the liquid surface level of the liquid is apreferable implementation of the present invention.

[0038] Also, moreover, placing the light radiating means on an outerwall of a vessel having an optically transmitting property and detectingthe liquid surface level of the liquid accommodated in the vessel ispreferable implementation of the present invention.

[0039] Also, moreover, including a fixing means for enabling the lightradiating means to be fixed on the wall of the vessel is a preferableimplementation of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

[0040]FIG. 1 is a diagrammatic view showing a usage state of a liquidsurface level detecting apparatus in the present invention;

[0041]FIG. 2 is a sectional view showing a first embodiment according tothe liquid surface level detecting apparatus in the present invention;

[0042]FIG. 3 is a diagrammatic view in which a vicinity of a liquidsurface level detecting unit of the liquid surface level detectingapparatus in the present invention shown in FIG. 2 is enlarged;

[0043]FIG. 4 is a diagrammatic graph showing a change in a lightreception amount of a light receiving means when the liquid surfacelevel detecting apparatus in the present invention detects a liquidsurface;

[0044]FIG. 5 is a sectional view showing a second embodiment accordingto the liquid surface level detecting apparatus in the presentinvention;

[0045]FIG. 6 is a sectional view showing a third embodiment according tothe liquid surface level detecting apparatus in the present invention;

[0046]FIG. 7 is a sectional view of an example of a conventional liquidsurface level detecting apparatus that uses a reflection of a light by aprism;

[0047]FIG. 8 is a sectional view of an example of a conventional liquidsurface level detecting apparatus that uses a total reflection light;

[0048]FIG. 9 is a sectional view of an example of a conventional liquidsurface level detecting apparatus that uses a scattering light;

[0049]FIG. 10 is a sectional view of another example of the conventionalliquid surface level detecting apparatus that uses the scattering light;

[0050]FIG. 11 is a diagrammatic view showing a first example of a usagestate of the liquid surface level detecting apparatus in the presentinvention;

[0051]FIG. 12A is a diagrammatic view showing a first example of placingliquid surface level detecting units at different heights, in the liquidsurface level detecting apparatus in the present invention;

[0052]FIG. 12B is a diagrammatic view showing a second example ofplacing the liquid surface level detecting units at different heights,in the liquid surface level detecting apparatus in the presentinvention;

[0053]FIG. 12C is a diagrammatic view showing a third example of placingthe liquid surface level detecting units at different heights, in theliquid surface level detecting apparatus in the present invention;

[0054]FIG. 13 is a sectional view showing a fourth embodiment accordingto the liquid surface level detecting apparatus in the presentinvention;

[0055]FIG. 14 is a view of a case that a plurality of glass opticalfibers of the liquid surface level detecting apparatus shown in FIG. 13are installed, and an X-Y sectional view of FIG. 13; and

[0056]FIG. 15 is a diagrammatic view showing a second example of theusage state of the liquid surface level detecting apparatus in thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0057] <First Embodiment>

[0058] With reference to the drawings, the liquid surface leveldetecting apparatus in the present invention will be described below. Atfirst, the first embodiment according to the liquid surface leveldetecting apparatus in the present invention is described. FIG. 1 is adiagrammatic view showing a usage state of the liquid surface leveldetecting apparatus in the present invention, and FIG. 2 is a sectionalview showing the first embodiment according to the liquid surface leveldetecting apparatus in the present invention. By the way, FIG. 2 is anenlarged view of a dotted line section in FIG. 1. In a liquid surfacelevel detecting apparatus 10 in the present invention, by inserting apole-shaped section approximately vertically from above a vessel, forexample, such as a tank or the like, and bringing a liquid 17 intocontact with a liquid surface level detecting unit placed at a lowportion, it carries out a liquid surface level detection.

[0059] The liquid surface level detecting apparatus 10 shown in FIG. 2has the total length of approximately several ten cm, and it is providedwith: an optically transmitting member (a light radiating means, anoptically transmitting means) 11 which is hollow and made of bar-shapedfluoro-resin or glass and the like; a light emitting means 12 composedof optical fibers, light emitting diodes (LED) and the like which areplaced in the hollow section therein; a light receiving means 13 forconverting an optical energy into an electrical energy such as anelectrical signal and the like; a light shielding wall (a lightshielding means) 14 for preventing a light from the light emitting meansfrom being directly irradiated to the light receiving means 13; an IC(Integrated Circuit) 15 for measuring a light amount received by thelight receiving means 13 and outputting its measured result; and a lightscattering member (a light scattering means, silicon rubber) 16 thatcovers the entire tips of the light emitting means 12 and the lightreceiving means 13 and has a property of scattering the irradiatedlight. By the way, for example, if the light emitting means 12 is theoptical fiber, it is connected to a light supplying means, and if thelight emitting means 12 is the light emitting diode, it is connected toa power source and the like. Also, as the light scattering member 16,the silicon rubber 16 having an adhesive property for fixing the lightemitting means 12 or the light receiving means 13 is suitable, and inparticular, a semi-transparent soft silicon sealant having a moistureabsorption hardening property and a heat-resisting property is optimal.

[0060] By the way, the wavelength of the light used in this liquidsurface level detection is not especially limited, and it is possible touse a visible region, an infrared region, an ultraviolet region and theother regions. Also, it is possible to place a prism and the like, andassign a directivity to the light from the light emitting means 12 orthe light received by the light receiving means 13, and efficientlycarry out the light emission or the light reception. Also, as theoptically transmitting member 11, it is desirable to use thefluoro-resin that is high in durability against chemicals, such as PTFE(poly-tetra-fluoro-ethylene), PFA (per-fluoro-alkoxy), FEP(fluorescent-ethylene-propylene), ETFE (ethylene-tetra-fluoro-ethylene)and the like. In particular, it is desirable to use the PTFE that isstable and not melted even at a high temperature, the PFA that is cheapand easy to process, and the like. Also, since the opticallytransmitting member 11 has the optically transmitting property andserves as the liquid surface level detecting unit for radiating thelight to external environment, the optically transmitting member 11 maybe referred to as the light radiating means 11. Also, the opticallytransmitting member has only the role of protecting the apparatus fromthe external environment. Thus, even if the light scattering means 16 isdirectly exposed to the external environment (namely, the opticallyradiating means 11 and the light scattering means 16 are integrated intothe same means) without placing the optically transmitting member 11 inthe vicinity of the liquid surface level detecting unit, it is possibleto attain the object of the present invention.

[0061]FIG. 3 is a diagrammatic view in which the vicinity of the liquidsurface level detecting unit of the liquid surface level detectingapparatus in the present invention shown in FIG. 2 is enlarged. Withreference to FIG. 3, the operation of the liquid surface level detectionand the flow of the light are described. For example, the material suchas the silicon rubber 16 is the semi-transparent material in which alarge number of particles are irregularly sporadic, and when the lightis irradiated to the silicon rubber 16, the light is scattered withinthe silicon rubber 16. Thus, the light irradiated from the lightemitting means 12 is scattered by the particles within the siliconrubber 16 and expanded in random directions. Then, the scattering lightrepeats the scattering caused by the particles, and for example, againreturns to the direction in which the light emitting means 12 exists, orgoes to the inner wall of the optically transmitting member 11. By theway, instead of the silicon rubber 16, it is also possible to use thematerial or member having the property of scattering the irradiatedlight.

[0062] Also, the light shielding wall 14 is designed such that the lightreceiving means 13 does not directly receive the light from the lightemitting means 12. Consequently, it is possible to avoid the light frombeing directly irradiated from the light emitting means 12 to the lightreceiving means 13 and possible to shield the light that is obstructiveof the liquid surface level detection. By the way, the meaning that thelight is not directly irradiated to the light receiving means 13 fromthe light emitting means 12 is such that the light emitting means 12 andthe light receiving means 13 are relatively placed so as not to directlyirradiate the light, irrespectively of the presence or absence of thesilicon rubber 16. Also, by establishing a predetermined angle andplacing the light emitting means, it is possible to increase the averageirradiation light amount to the vicinity of one unit (hereafter,referred to as the liquid surface level detecting unit) of the opticallytransmitting member 11 that radiates a part of the scattering light tothe outside between the light emitting means 12 and the light receivingmeans 13. Similarly, by establishing a predetermined angle and placingthe light receiving means, it is possible to increase the efficiency ofthe light reception and possible to improve the precision in the liquidsurface level detection.

[0063] Moreover, even by giving an inclination to the light shieldingwall 14 and making it serve as the role of a light reflection plate orindependently placing the light reflection plate, similarly, it ispossible to improve the precision in the liquid surface level detection.By the way, the length of this liquid surface level detecting unit isapproximately several mm. Also, in order to protect the light from beingabsorbed by the light shielding wall 14, by painting the light shieldingwall 14 white, or covering with film such as silver, aluminum and thelike, it is possible to increase a light reflectance factor of the lightshielding wall 14.

[0064] The light reaching the inner wall of the optically transmittingmember 11, although a part thereof is reflected by the inner wall, istransmitted through the inside of the optically transmitting member 11,and reaches the outer wall of the optically transmitting member 11. Ifthe liquid 17 does not exist in the outside (the external environment)of the optically transmitting member 11 (namely, if the outside is theair), the input light of the angle smaller than the critical angle withrespect to a normal line to the outer wall of the optically transmittingmember 11 is transmitted through the boundary of the outside andradiated to the outside (however, the part thereof is reflected by theouter wall). On the other hand, the input light of the angle equal to orgreater than the critical angle brings about the total reflection on theouter wall. By the way, on the inner wall and outer wall of theoptically transmitting member 11, the traveling route of the light obeysthe law of the reflection refraction on its boundary. By the way, thefluoro-resin such as the PFA and the like is not strictly said to betransparent (namely, it is semi-transparent), and it has the property ofscattering the light. However, for the purpose of simple explanation,here, the explanation of its effect is ignored.

[0065] The light, which is reflected by the inner wall or outer wall ofthe optically transmitting member 11 and returned to the inside of theoptically transmitting member 11, further repeats the scattering withinthe silicon rubber 16 existing in the inside of the opticallytransmitting member 11 and the reflection on the light shielding wall14. As a result, there is also the light which again reaches the outerwall of the optically transmitting member 11 and is transmitted throughthe outer wall and radiated to the outside. In this way, the lightirradiated by the light emitting means 12 is roughly divided into thetwo lights of the light, which is scattered by the silicon rubber 16 andfinally sent out to the outside of the optically transmitting member 11,and the light which is returned to the inside of the opticallytransmitting member 11. And, a part of the light, which repeats thescattering in the inside of the optically transmitting member 11, isreceived by the light receiving means 13. By the way, since thescattering light has the random direction, the average light amount at astatic state is constant, and the radiation light amount (the averageradiation light amount) to the outside of the optically transmittingmember 11, the light amount (the average light reception amount)received by the light receiving means 13 are constant.

[0066] As mentioned above, if the external environment is not changed,the light reception amount received by the light receiving means 13 isconstant. However, for example, such as the case that the rise in aliquid surface 18 causes the liquid surface to approach the liquidsurface level detecting unit (or the case that the opticallytransmitting member 11 is inserted into the liquid 17) and the like, thechange in the external environment leads to the change in the lightreception amount of the light receiving means 13.

[0067] Also, the light reception amount of the light receiving meanslargely depends not only on the refractive index of the liquid 17 in theoutside, but also on the absorption reflection spectral property of theliquid 17. For example, the white liquid such as milk and the like, theliquid metal such as silver and the like have the property of reflectingthe visible region light. In such a case, it is possible to carry outthe liquid surface level detection by selecting a wavelength region of alight to be used, on the basis of the absorption reflection spectralproperty of the liquid targeted for the liquid surface level detection.

[0068]FIG. 4 is a diagrammatic graph showing the change in the lightreception amount of the light receiving means when the liquid surfacelevel detecting apparatus in the present invention detects the liquidsurface. If the liquid 17 having the refractive index greater than theair is raised and the liquid surface 18 reaches the liquid surface leveldetecting unit, a part of the scattering light reflected by the outerwall of the optically transmitting member 11 until that time is radiatedinto the liquid 17. That is, refractive indexes of mediums existing inthe external environment become greater, and the light reflectiontransmittance property on the boundary between the liquid 17 and theoptically transmitting member 11 is changed, thereby increasing thelight amount to be radiated into the mediums. As a result, the lightamount, which is reflected by the boundary between the liquid 17 and theoptically transmitting member 11 and returned to the inside of theoptically transmitting member 11, is reduced, thereby reducing the lightreception amount of the light receiving means 13. In this way, bymeasuring the change in the light reception amount attenuated at thetime of the propagation, it is possible to detect the liquid surfacelevel of the liquid 17.

[0069] As mentioned above, according to the first embodiment, the lightirradiated from the light emitting means 12, since scattered within thesilicon rubber 16, has the effect similar to the light emitted to therandom directions from a large number of light sources. Consequently,the range in which the liquid surface level is detected (the range inwhich the light is emitted to the outside, and the range in which thelight once outputted to the outside is returned) becomes very wide.Then, even if the liquid drops and the liquid films are deposited on thevicinity of the liquid surface level detecting unit, it is possible toignore those influences, and measure the change in the light amount inassociation with the variation in the liquid surface level, and surelycarry out the liquid surface level detection.

[0070] Also, for example, by establishing that the IC 15 outputs asignal indicative of the liquid surface level detection if the lightreception amount of the light receiving means 13 becomes a predeterminedlight reception amount (a standard light reception amount) or less, itis possible to report the liquid surface level detection to the outside.By the way, for example, it is desirable that an adjusting means, suchas a trimmer and the like, can be used to simply adjust thepredetermined light reception amount. Then, by enabling the differentpredetermined light reception amount to be established on the basis of akind of a liquid, it is possible to carry out the liquid surface leveldetections of the liquids of the various kinds. Also, by establishing aplurality of values as the predetermined light reception amounts, it isalso possible to detect the respective boundaries of the liquids 17composed of a plurality of layers. Also, for example, when the variationin the light reception amount of the light receiving means 13 ismeasured, if there is the variation of a predetermined value or more, itis possible to establish that the IC 15 outputs the signal indicative ofthe liquid surface level detection.

[0071] Also, in the liquid 17 having the property of reflecting thelight such as the above-mentioned white liquid and the like, when itsliquid surface 18 reaches the liquid surface level detecting unit, thelights radiated to the outside of the optically transmitting member 11until that time are all returned, thereby increasing the light receptionamount of the light receiving means 13. Thus, for example, byestablishing that the IC 15 outputs the signal indicative of the liquidsurface level detection if the light reception amount of the lightreceiving means 13 becomes the predetermined light reception amount ormore, it is possible to report the liquid surface level detection to theoutside.

[0072] Also, since the variation in the light reception amount of thelight receiving means 13 is the measurement target, it is not necessaryto strictly define the installation positions of the light emittingmeans 12 and the light receiving means 13, and they may be installedsuch that the light from the light emitting means 12 can be received bythe light receiving means 13. This is the point which is largelydifferent from the fact that in the conventional liquid surface leveldetecting apparatus for measuring the presence or absence of the totalreflection as shown in FIG. 8, the installation positions of the lightemitting means 202 and the light receiving means 203 need to be strictlydefined in accordance with the critical angle of the total reflection.Also, preferably, the installations are implemented such that thedirectivity to the vicinity of the liquid surface level detecting unitis assigned to the light emitting means 12 and the light receiving means13, the light from the light emitting means 12 is efficiently irradiatedto the vicinity of the liquid surface level detecting unit, and thelight emitted from the vicinity of the liquid surface level detectingunit can be efficiently received by the light receiving means 13.

[0073] Also, in the above-mentioned first embodiment, by adhering thesilicon rubber 16 to the light emitting means 12 and the light receivingmeans 13 in addition to the entire vicinities of the liquid surfacelevel detecting units, it is possible to fix the light emitting means12, the light receiving means 13, the light shielding wall 14 and thelike with the silicon rubber 16. In particular, the silicon rubber 16has the high adhering property to the fluoro-resin such as the PFA, thePTFE and the like. Thus, it is possible to stably install the respectivemeans of the vicinity of the liquid surface level detecting unit. As aresult, it is possible to stabilize the operation of the liquid surfacelevel detection.

[0074] <Second Embodiment>

[0075] The second embodiment according to the liquid surface leveldetecting apparatus in the present invention will be described below.FIG. 5 is a sectional view showing the second embodiment according tothe liquid surface level detecting apparatus in the present invention.The liquid surface level detecting apparatus 10 in the present inventionshown in FIG. 5 is provided with an optically transmitting member 21, alight emitting means 22, a light receiving means 23, a light shieldingwall 24 and a silicon rubber 26, similarly to the liquid surface leveldetecting apparatus in FIG. 2. However, this is designed such that thesilicon rubber 26 exists only in the vicinity of the light emittingmeans 22.

[0076] This liquid surface level detecting apparatus 10 in the presentinvention shown in FIG. 5 is designed such that the silicon rubber 26makes the light from the light emitting means 22 serve as the scatteringlight, and the scattering light is irradiated to the liquid surfacelevel detecting unit. The light returned by the reflection by the liquidsurface level detecting unit is propagated toward the light receivingmeans 23 while repeating the reflection, for example, at the intervalbetween the light shielding wall 24 and the optically transmittingmember 21. Thus, the liquid surface level detection by the lightreceiving means 23 becomes possible. Hence, similarly to the liquidsurface level detecting apparatus 10 explained in the first embodimentshown in FIG. 2, it is possible to irradiate the scattering light to theliquid surface level detecting unit. By measuring the change in thelight reception amount of the light receiving means 23, it is possibleto carry out the liquid surface level detection of the liquid 17.

[0077] As mentioned above, according to the second embodiment, the lightirradiated from the light emitting means 22, since scattered within thesilicon rubber 26 placed in the light emitting means 22, has the effectsimilar to the light emitted to the random directions from the largenumber of light sources. Consequently, the range in the detection of theliquid surface level becomes very wide. Even if the liquid drops and theliquid films are deposited on the vicinity of the liquid surface leveldetecting unit, it is possible to ignore those influences, and measurethe change in the light amount in association with the variation in theliquid surface level, and surely carry out the liquid surface leveldetection.

[0078] <Third Embodiment>

[0079] Moreover, the third embodiment according to the liquid surfacelevel detecting apparatus in the present invention will be describedbelow. FIG. 6 is a sectional view showing the third embodiment accordingto the liquid surface level detecting apparatus in the presentinvention. The liquid surface level detecting apparatus 10 in thepresent invention shown in FIG. 6 is provided with an opticallytransmitting member 31, a light emitting means 32, a light receivingmeans 33, a light shielding wall 34 and a silicon rubber 36, similarlyto the liquid surface level detecting apparatus in FIG. 2. However, thisis designed such that the silicon rubber 36 exists only in the whole onthe inner wall (the vicinity of the liquid surface level detecting unit)of the optically transmitting member 31.

[0080] This liquid surface level detecting apparatus 10 in the presentinvention shown in FIG. 6 is designed such that the silicon rubber 36makes the light reaching the boundary between the liquid 17 and theoptically transmitting member 31 serve as the scattering light. Thus,similarly to the liquid surface level detecting apparatuses explained inthe first and second embodiments shown in FIG. 2 and FIG. 5, it ispossible to irradiate the scattering light to the liquid surface leveldetecting unit. By measuring the change in the light reception amount ofthe light receiving means 33, it is possible to carry out the liquidsurface level detection of the liquid 17.

[0081] As mentioned above, according to the third embodiment, the lightirradiated from the light emitting means 32, since scattered within thesilicon rubber 36 placed on the entire inner wall of the opticallytransmitting member 31, has the effect similar to the light emitted tothe random directions from the large number of light sources.Consequently, the range in the detection of the liquid surface levelbecomes very wide. Even if the liquid drops and the liquid films aredeposited on the vicinity of the liquid surface level detecting unit, itis possible to ignore those influences, and measure the change in thelight amount in association with the variation in the liquid surfacelevel, and surely carry out the liquid surface level detection.

[0082] <Fourth Embodiment>

[0083] Moreover, the fourth embodiment according to the liquid surfacelevel detecting apparatus in the present invention will be describedbelow. FIG. 13 is a sectional view showing the fourth embodimentaccording to the liquid surface level detecting apparatus in the presentinvention. The liquid surface level detecting apparatus 10 in thepresent invention shown in FIG. 13 is provided with an opticallytransmitting member 41, a light emitting means 42, a light shieldingwall 44 and a silicon rubber 46, similarly to the liquid surface leveldetecting apparatus in FIG. 2. Also, as the light receiving means 13shown in FIG. 2, a glass optical fiber 51 is used. This glass opticalfiber 51 has a merit that it is strong in a high temperature and thelike, which will be described later.

[0084] Also, FIG. 14 is a view of a case that a plurality of glassoptical fibers of the liquid surface level detecting apparatus shown inFIG. 13 are installed, and an X-Y sectional view of FIG. 13. In thisway, the installation of the plurality of glass optical fibers 51enables those glass optical fibers 51 to receive the lights which arereflected by and returned from the liquid surface level detecting unit.

[0085] If an area of a light receiving section of light is small, in acase that water drops remain in the liquid surface level detecting unitor in other cases, an erroneous operation is easily induced. On theother hand, in a case of considering the scale and weight reductions inthe liquid surface level detecting apparatus 10, it is impossible toexcessively enlarge the light receiving section. So, in the forthembodiment, as shown in FIG. 14, for example, the plurality of (12 inFIG. 14) glass optical fibers 51 having a diameter of 1 mm are arrayed.Consequently, even if the water drops are deposited on the vicinity ofthe liquid surface level detecting unit, it is possible to ignore theinfluence of the water drops, and measure the change in the light amountin association with the variation in the liquid surface level, andsurely carry out the liquid surface level detection.

[0086] As mentioned above, according to the fourth embodiment, the lightirradiated from the light emitting means 42, since scattered within thesilicon rubber 46, has the effect similar to the light emitted to therandom directions from the large number of light sources. Consequently,the range in the detection of the liquid surface level becomes verywide. Even if the liquid drops and the liquid films are deposited on thevicinity of the liquid surface level detecting unit, it is possible toignore those influences, and measure the change in the light amount inassociation with the variation in the liquid surface level, and surelycarry out the liquid surface level detection.

[0087] Also, in particular, as shown in FIG. 14, by arraying the lightreceiving sections of the plurality of glass optical fibers 51 on asubstantially flat surface along the inner wall of the opticallytransmitting member 41, it is possible to detect the level of the liquidsurface, which is the substantially flat surface, at a high precision,and possible to protect the erroneous operation caused by the liquiddrops and the liquid films. By the way, FIG. 14 illustrates the arraypattern in which the light receiving sections of the plurality of glassoptical fibers 51 are arrayed along the inner wall of the opticallytransmitting member 41. However, the array pattern of the lightreceiving sections in the present invention is not limited to theabove-mentioned array pattern. For example, correspondingly to the shapeof the liquid surface level detecting apparatus 10, it is possible todetermine the array pattern of the plurality of light receivingsections. For example, as described later (FIG. 15), in the liquidsurface level detecting apparatus 10 that can carry out the liquidsurface level detection from the outside without dipping into theliquid, it is desired to prepare the array pattern corresponding to theshape of a pressurizing tank 91.

[0088] An application example of the liquid surface level detectingapparatus in the present invention as mentioned above will be describedbelow. FIG. 11 is a diagrammatic view showing a first example of a usagestate of the liquid surface level detecting apparatus in the presentinvention. By the way, a controller 90 for carrying out its operationcontrol and a process of a measurement result and the like is connectedto the liquid surface level detecting apparatus 10. A state at which theapparatus in the present invention is inserted into the liquid 17 withinthe pressurizing tank 91 is illustrated. By freely establishing a lengthof a pole-shaped section having the liquid surface level detecting unitin a low portion, it is possible to manufacture the liquid surface leveldetecting apparatus 10 that is easily usable depending on a situation.For example, in a gallon bottle for a drug, a pressuring tank, a pailcan and the like, the pole-shaped section is desired to have the longestlength of about 330 mm, and in a drum can and the like, the pole-shapedsection is desired to be about 80 mm.

[0089] Also, FIGS. 12A to 12C are diagrammatic views showing examples ofplacing the liquid surface level detecting units at different heights,in the liquid surface level detecting apparatus in the presentinvention. As shown in FIG. 12A and FIG. 12B, by placing a plurality ofpole-shaped sections having different heights, it is possible to carryout the liquid surface level detection at the different heights. By theway, in the liquid surface level detecting apparatus 10 shown in FIG.12A, the liquid surface level detection is possible at different twopoints, and in the liquid surface level detecting apparatus 10 shown inFIG. 12B, the liquid surface level detection is possible at differentfour points. Also, if the plurality of pole-shaped sections are placedin this way, the usage in a small tank becomes difficult. Thus, as shownin FIG. 12C, by placing the liquid surface level detecting units havingthe different heights in a single pole-shaped section, it is possible tominiaturize the liquid surface level detecting apparatus 10 due to theplurality of locations.

[0090] Also, FIG. 15 is a diagrammatic view showing a second example ofthe usage state of the liquid surface level detecting apparatus in thepresent invention. The usage example shown in FIG. 11 is designed so asto directly insert the liquid surface level detecting unit of the liquidsurface level detecting apparatus 10 in the present invention into theliquid 17 and detect the liquid surface 18. However, the usage exampleshown in FIG. 15 is designed so as to install the liquid surface leveldetecting unit in a level gage tube 93 of the pressurizing tank 91,which is typically used for a visual inspection of a liquid surfacelevel and the like, and detect the liquid surface 18. Consequently, ifit is difficult to dip the liquid surface level detecting unit into theliquid 17, or if the liquid 17 is a dangerous material (for example, amaterial having a high reactivity, or a material of a high temperatureor low temperature), without directly dipping into the liquid 17, it ispossible to detect the liquid surface level. By the way, in a case ofdetecting the liquid surface level of the liquid accommodated in thevessel (the pressurizing tank) 91 where the level gage tube 93 does notexist, it is also possible to directly install the liquid surface leveldetecting unit in the vessel 91.

[0091] Also, it is desirable to install a fixing means (a belt) 92 forfixing the liquid surface level detecting unit on the outer wall of thevessel 91 for accommodating the liquid. For example, by using the belt92 shown in FIG. 15 and wrapping the belt 92 around an outercircumference of the vessel, it is possible to fix the liquid surfacelevel detecting unit at a predetermined position of the vessel 91. Also,as the fixing means 92, an adhesive surface having a viscosity isplaced. Then, by using this adhesive surface, the liquid surface leveldetecting unit can be pasted on the vessel 91.

[0092] Also, as shown in FIG. 15, a silicon rubber 56 can be directlyapplied to the outer wall of the vessel 91. This leads to the meritsthat there is no leakage of the light from gap and the like (opticaladhesiveness), and due to the viscosity of the silicon rubber 56, thereis no displacement, and sticking on the outer wall of the vessel 91 ispossible without using the belt 92, and the invasion of the liquid intothe outer wall between the vessel 91 and the silicon rubber 56 can beprotected, and the erroneous operation is protected. Also, by using thesilicon rubber curing solution of the same property, it is also possibleto adhere the liquid surface level detecting unit and the vessel 91.

[0093] Also, there is a case that the liquid targeted for the liquidsurface level detection and the operation environment are at a hightemperature. In particular, if the liquid is oil and the like, there maybe a case that the liquid surface level of the liquid close to about200° C. needs to be detected. However, for example, when an LED lightsource of a semiconductor is used for the light emitting means 12, 22,32 or 42, if it exceeds about 80° C., the LED light source is brokenwhich disables the detecting operation. In view of the operation at thetime of such a high temperature, by using a small precise lamp (atungsten lamp) as the light emitting means 22 and by using the glassoptical fiber as the light receiving means 13, 23 or 33, it isexcellently operated even at the time of the high temperature of about300° C., thereby insuring the liquid surface level detecting operationat the time of the high temperature.

INDUSTRIAL APPLICABILITY

[0094] As mentioned above, according to the present invention, byplacing a light shielding means so as not to directly irradiate thelight from the light emitting means to the light receiving means, thepart of the scattering light scattered by the light scattering means isradiated to the outside of the scattering means or the lighttransmitting means in the liquid surface level detecting unit of thelight radiating means. On the other hand, the scattering light which isreflected and returned without being radiated is received by the lightreceiving means, and the change in its light reception amount isdetected. Thus, the usage is possible in the various detection targetsand usage environments without selecting the detection target. It ispossible to efficiently irradiate the light to the liquid surface leveldetecting unit, and detect the variation in the light reception amountof the light receiving means at the high sensibility. It is possible toattain the liquid surface level detecting apparatus, which is excellentin the durability, easy to manufacture, and can be actually used.

1. A liquid surface level detecting apparatus for detecting a liquidsurface level of a liquid existing in an outside, including: a lightemitting means for emitting a light; an optically scattering means forscattering the light emitted by said light emitting means; a lightradiating means having a liquid surface level detecting unit forradiating a part of a scattering light scattered by said opticallyscattering means to an outside of said optically scattering means; alight receiving means for receiving said scattering light which isreflected by and returned from a boundary of the outside of saidoptically scattering means or said light radiating means without beingradiated by said light radiating means; and a light shielding means forshielding the light so that the light from said light emitting means isnot directly irradiated to said light receiving means, wherein if saidliquid exists in said outside, a radiation light amount to the outsideof said light radiating means is changed, and that change is detected onthe basis of the light reception amount of said light receiving means,thereby detecting said liquid surface level of said liquid.
 2. Theliquid surface level detecting apparatus according to claim 1,characterized by establishing a predetermined angle and placing saidlight emitting means or light receiving means.
 3. The liquid surfacelevel detecting apparatus according to claim 1, characterized by placinga plurality of said light receiving means.
 4. The liquid surface leveldetecting apparatus according to claim 3, characterized by arraying saidplurality of light receiving means on a substantially flat surface. 5.The liquid surface level detecting apparatus according to claim 1,characterized by covering said light shielding means with a film forlight reflection, in order to protect the light from being absorbed bysaid light shielding means.
 6. The liquid surface level detectingapparatus according to claim 1, characterized by enabling a standardlight reception amount in said light receiving means to be establishedon the basis of a kind of said liquid, and comparing the light receptionamount of said light receiving means with said standard light receptionamount, and consequently detecting said liquid surface level of saidliquid.
 7. The liquid surface level detecting apparatus according toclaim 1, characterized by placing said optically scattering means arounda light emitting unit of said light emitting means.
 8. The liquidsurface level detecting apparatus according to claim 1, characterized byplacing said optically scattering means around said liquid surface leveldetecting unit to which said light from said light emitting means isirradiated.
 9. The liquid surface level detecting apparatus according toclaim 1, characterized in that said optically scattering means issilicon rubber.
 10. The liquid surface level detecting apparatusaccording to claim 1, characterized in that said light radiating meansis per-fluoro-alkoxy.
 11. The liquid surface level detecting apparatusaccording to claim 1, characterized by using a tungsten lamp as saidlight emitting means and using a glass optical fiber as said lightreceiving means.
 12. The liquid surface level detecting apparatusaccording to claim 1, characterized by dipping said light radiatingmeans into said liquid and detecting said liquid surface level of saidliquid.
 13. The liquid surface level detecting apparatus according toclaim 1, characterized by placing said light radiating means on an outerwall of a vessel having an optically transmitting property and detectingsaid liquid surface level of said liquid accommodated in said vessel.14. The liquid surface level detecting apparatus according to claim 13,characterized by including a fixing means for enabling said lightradiating means to be fixed on the wall of said vessel.